Automotive Air Conditioning Information Forum

Auto A/C for beginners 2.0
This is a new to me 2003 Freightliner FLD120 The A/C leaked when I bought it, if you charged it, it blew cold air but it leaked out in a day or 3.
134a
I fixed the leaks I found, replaced the filter dryer, and the Schrader valves. I tried to pump the system down but it wouldn’t hold a vacuum.
I pressurized it with 50# of nitrogen and it held all night. So I tried to pump it down again. It pumps down to 20, but as soon as you close the valves it comes back to 0 within 30 seconds.
I pressurized it to 150# and did soap bubble tests, I found no leaks and the pressure held for 24 hours. But, it wasn’t always balanced on the gauges, sometimes the high side would be above 150 and the low side below, and other times the high side was low and the low side was higher. I thought maybe there was oil trapped or a blockage so I changed the Expansion valve and flushed out the evaporator.
I put the vacuum pump back on and the same issue. It won’t pull down after 1.5 2 hours, and comes back to 0 in seconds.
I need some advice. Why does it hold pressure, but not a vacuum?

Maybe there is still oil/freon trapped in the condenser?
Honestly, short of replacing the condenser and compressor next, I’m not sure what else to do.

One way leaks are common and drive you nuts.
I'd puff in a little 134 the best you can maybe 20 psi and use an electronic sniffer to sniff everything. Don't forget to put it in the drain tube of the evap.
Be sure your gauge set and couplers are tight; the seals at the knurled ends can be changed out

tbirdtbird wrote: ↑Thu Jun 17, 2021 10:38 am One way leaks are common and drive you nuts.

One of the reasons why diagnosing and repairing MVAC often can be mystifying, time consuming, and expensive.

tbirdtbird wrote: ↑Thu Jun 17, 2021 10:38 am Be sure your gauge set and couplers are tight; the seals at the knurled ends can be changed out

Checking your manifold gauge set and hoses is always a great idea before hooking things up. However, it does seem like the leak is in the system someplace because the refrigerant leaks out even with the gauges disconnected.

tbirdtbird wrote: ↑Thu Jun 17, 2021 10:38 am I'd puff in a little 134 the best you can maybe 20 psi and use an electronic sniffer to sniff everything. Don't forget to put it in the drain tube of the evap.

In looking for the source of the leak...and if you haven't already done this...try placing a shower cap over the front end of the compressor / clutch assembly. You'll have to remove the belt(s) from the clutch pulley first. Let it set like that for an hour or so, then use your sniffer to probe inside the shower cap. If the sniffer alerts, it's probably the compressor shaft seal that's leaking.

It was a bad compressor